The present invention relates to a lockup clutch of a torque converter for a motor vehicle, and more particularly to a structure for mounting the lockup clutch.
A lockup clutch of a torque converter is generally disposed in a converter cover between the cover and a turbine. The lockup clutch having a lockup piston integral with a torsion damper is slidably mounted on a turbine hub of the turbine. The lockup clutch is brought into lockup state or release state by controlling oil pressures applied to oil chambers on opposite sides of the piston so as to engage and disengage the piston with the converter cover.
Japanese patent application laid open No. 57-51056 and Japanese utility model application laid open No. 59-163260 disclose structures for mounting such a lockup clutch. A hub of the turbine is slidably splined to an input shaft at the front end thereof in the same manner as the torque converter without the lockup clutch. The turbine hub supports the lockup piston and the torsion damper as well as the turbine.
However, the input shaft is supported at a rear end but not at the front end where the turbine hub is mounted. Thus, the weight of the lockup clutch on the front end of the input shaft in addition to the weight of the turbine and unbalanced load of the lockup clutch turbine cause the shaft to oscillate when the lockup piston is not in contact with the converter cover. The oscillation is transmitted to a stator shaft surrounding the input shaft. The stator shaft is subjected to bending stress in addition to torque from the stator of the torque converter. Thus, stress at a supporting portion of the stator shaft becomes large.
The stator shaft is usually made of cast iron since it is generally formed integral with a cover of an oil pump and has oil passage therein and ports for the oil passages. Accordingly, the stator shaft tends to break at the base due to the above-described stress. In addition, in a transaxle type transmission system having a differential device in a space between the torque converter and an automatic transmission, the stator shaft becomes longer, resulting in significant damage, in accordance with the stress.
In another mounting structure, the front end of the input shaft is axially slidably supported by the converter cover through a bearing for the convenience of assembly of the converter. In such a torque converter, radial passages to a release side oil chamber are formed in the input shaft. While the lockup clutch is locked, oil is not supplied to the release side chamber, thereby urging the lockup piston to the converter cover. Therefore, oil passages in the input shaft communicated with the release side chamber are thus obstructed by the bearing.
Accordingly, when release oil is supplied to the chamber passing through the passages, the oil flow is reduced by the passages. As a result, the release of the lockup clutch is delayed, and causes a shock when changing the transmission ratio.